Estimation of genetic relationship for the efficient genetic resources utilization in the breeding programs of guineagrass (Panicum maximum Jacq.) is of utmost importance. Thirteen simple sequence repeat (SSR) markers, developed from genomic and cDNA clones, were successfully employed for estimating genetic relationship in guineagrass based on the analysis of 77 accessions. A genomic library enriched for (AG)/(TC) and expressed sequence tag (EST) sequences were screened for repeat motifs in guineagrass. A total of 13 SSR markers including eight from genomic clones and five from EST, were developed. Of these, eight, four and one SSR markers have perfect, interrupted and compound repeat motifs, respectively. One SSR has trinucleotide repeat motif of AGT, whereas the other 12 markers have dinucleotide motif of AG. The 13 SSR primer sets produced 1–4 amplified fragments within accessions, putatively corresponding to alleles derived from autotetraploidy of guineagrass. One hundred and ninety putative alleles were generated by 13 SSR in the 77 guineagrass accessions assayed. The values of power of discrimination (PD) ranged 0.449–0.968 with an average value of 0.859. Polymorphic information content (PIC) ranged 0.399–0.951. A phenogram of 77 guineagrass accessions obtained based on the genetic similarity with 13 SSR, revealed six major groups. The results suggested that the center of original region of guineagrass is Kenya, which agrees with an earlier study based on morphological analysis. The wide distribution of the guineagrass accessions strongly supports the assumption of intercrossing with the diploid sexual materials in natural habitat.

In vitro dry matter digestibility (IVDMD) is one of the most important traits for grass quality improvement. Analysis of IVDMD in laboratory with a large number of breeding populations is very laborious. The objectives of this study were to evaluate IVDMD of brachiariagrass germplasm as material in breeding program, and also to determine the appropriate selection criteria for high digestibility. IVDMD (pepsin‐cellulase method), morphology traits and water content of 17 genotypes of Brachiaria spp. (B. brizantha, B. decumbens, B. ruziziensis and Brachiaria hybrid) were evaluated at two harvesting times, winter and early summer seasons. The correlations among traits were determined, and their heritability were also estimated. IVDMD ranged from 48.9 to 59.0% in winter, and 42.9 to 54.4% in early summer. Among morphological traits, leaf‐stem index (ratio of leaf width/stem diameter) showed the highest correlation with whole plant IVDMD (r = 0.74) followed by leaf‐shape ratio (leaf width/leaf length; r = 0.72), and leaf water content also highly correlated with whole plant IVDMD (r = 0.79). The broad sense heritability of IVDMD and the related traits of two harvests combination were high with the range of 0.75–0.93. The results demonstrate that leaf‐stem index, leaf‐shape ratio and water content could be the useful selection criteria for the breeding of brachiariagrass for high digestibility.

Tropical grasses have been widely utilized as warm-season grasses in the warm temperate zone since the early 20th century because of their high yields as well as for perennial forages in their native tropical areas. The high yield of tropical grasses is mainly due to C4 photosynthesis. However, the soaring demands for animal production sparked by economic development in tropical countries mean genetic improvement of such grasses is urgently needed. Considerable breeding efforts have been made to create and develop new tropical grass cultivars, although direct selection from natural populations remains the main method used for breeding. Cross-breeding has not proliferated due to a lack of genetic information concerning the polyploidy, high sterility, outcrossing, and apomixis of these grasses, although several of these difficulties are starting to be resolved by advanced research using molecular biology tools. These tools are an effective means of achieving genetically improving of tropical grasses, and further development is anticipated. In this review, achievements in the improved guineagrass, brachiariagrass, sorghum, and zoysiagrass are introduced and discussed.

Guinea grass (Panicum maximum Jacq.) is an important C-4 perennial plant that grows in southern Japan. In March 2010, a smut disease was found in grass that is cultivated in the Ishigaki Islands, Okinawa, in southernmost Japan. Spikelets of susceptible cultivars were swollen and filled with gray spore masses and seed production was substantially reduced. Two single-spore isolates of a smut fungus were obtained from infected spikelets and deposited at the NIAS Genebank, Japan as MAFF511519 and 511520. The 28S rDNA sequences of the isolates were analyzed as described by Boekhout et al. (1). The 28S rDNA sequence (GenBank Accession No. AB647346) of isolate MAFF511519 matched that of Conidiosporomyces ayresii (GenBank Accession No. AY819017) isolated from P. maximum with 99.8% similarity. Spores were pale brown to brown, globose to subglobose, verrucose, and 14 to 16 × 15 to 18 μm in diameter with relatively thick walls of 2 to 3 μm. With scanning electron microscopy, warts appeared dense and short with pointed tips. Spores germinated under wet conditions and produced masses of basidiospores. Basidiospores were aseptate, long, cylindrical, straight to slightly curved, 20 to 37 × 2 to 3 μm, and often germinated into Y-shaped conidia. This description matches previous descriptions (3) of C. ayresii (Berk.) Vánky (Tilletia ayresii Berk.) of the smut pathogen of guinea grass (2). The smut fungus was identified as C. ayresii on the basis of morphology and molecular phylogenetic analysis. To produce inoculum, the isolates were grown on potato dextrose agar at 25°C in the dark for 7 days. Two plants of cv. Ryukyu 5-gou with half-flowering heads were grown in a greenhouse for approximately 1 month and then inoculated by atomizing them with conidial suspensions of each isolate (106 conidia/ml). A plant sprayed with sterilized distilled water served as the control. Inoculated heads were covered with plastic bags for 48 h at 25°C. After 30 days, all inoculated plants were symptomatic with swollen spikelets releasing gray spores. Controls remained asymptomatic. The smut fungus was reisolated from released gray spores, confirming Koch's postulates. To our knowledge, this is the first report of smut caused by C. ayresii on guinea grass in Japan. References: (1) T. Boekhout et al. Stud. Mycol. 38:175, 1995. (2) J. M. Lenné and P. Trutmann. Diseases of Tropical Pasture Plants. CAB International, Wallingford, UK, 1994. (3) K. Vánky and R. Bauer. Mycotaxon 43:427, 1992.